Lithographic systems and methods of operating the same

ABSTRACT

A lithographic system for projecting an image onto a workpiece using radiation is provided. The lithographic system includes: a support structure for supporting a workpiece; a radiation source for providing radiation to project an image on the workpiece; a reticle positioned between the radiation source and the workpiece; and a mask positioned adjacent the reticle, the mask being configured to block radiation from the radiation source, the mask including a heat removal apparatus.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/600,956 filed Oct. 1, 2021, which claims the benefit of InternationalApplication No. PCT/EP2020/055074 filed Feb. 26, 2020, which claimspriority to U.S. Provisional Application No. 62/831,381, filed Apr. 9,2019, the content of all of which are incorporated herein by reference.

FIELD

The invention relates to lithographic systems, and more particularly, tosystems and methods addressing heat in the area of the reticle of thelithographic system.

BACKGROUND

In lithography applications, radiation provided by a radiation source isused to expose fields on a workpiece (e.g., a wafer). Often, it isdesired to expose not only full fields on the workpiece, but alsopartial fields (e.g., for alignment marks on the workpiece).

Conventional systems (including some form of reticle masking) are shownin, for example: U.S. Pat. Nos. 6,348,303; 7,382,439. Such systemsinclude reticle masking using blades in the illuminator of the system,and not adjacent the reticle.

Certain conventional lithographic systems include reticles having alight blocking layer (e.g., a chromium layer), where the layer absorbs apart of the radiation from a radiation source of the lithographicsystem. This radiation absorption causes the reticle to heat up, therebydeforming the reticle by thermal expansion, consequently resulting in adeformation of the pattern that is projected onto a workpiece.

Thus, it would be desirable to provide improved lithographic systems(and related methods) overcoming one or more of the deficiencies ofconventional systems.

SUMMARY

According to an exemplary embodiment of the invention, a lithographicsystem for projecting an image onto a workpiece using radiation isprovided. The lithographic system includes: a support structure forsupporting a workpiece; a radiation source for providing radiation toproject an image on the workpiece; a reticle positioned between theradiation source and the workpiece; and a mask positioned adjacent thereticle, the mask being configured to block radiation from the radiationsource, the mask including a heat removal apparatus.

According to another exemplary embodiment of the invention, anotherlithographic system for projecting an image onto a workpiece usingradiation is provided. The lithographic system includes: a supportstructure for supporting a workpiece; a radiation source for providingradiation to project an image on the workpiece; a reticle positionedbetween the radiation source and the workpiece; and a mask positionedadjacent the reticle, the mask being configured to block radiation fromthe radiation source, wherein the mask includes a body portion and aradiation absorbing coating applied to at least a portion of an externalsurface of the body portion.

According to yet another exemplary embodiment of the invention, anotherlithographic system for projecting an image onto a workpiece usingradiation is provided. The lithographic system includes: a supportstructure for supporting a workpiece; a radiation source for providingradiation to project an image on the workpiece; a reticle positionedbetween the radiation source and the workpiece; and a mask positionedadjacent the reticle. The mask is configured to block radiation from theradiation source. The mask defines an illumination area of an image tobe projected onto the workpiece using a pattern of the reticle andradiation from the radiation source. The illumination area defined bythe mask is variable.

According to yet another exemplary embodiment of the invention, anotherlithographic system for projecting an image onto a workpiece usingradiation is provided. The lithographic system includes: a supportstructure for supporting a workpiece; a radiation source for providingradiation to project an image on the workpiece; a reticle positionedbetween the radiation source and the workpiece; and a mask positionedadjacent the reticle. The mask is configured to block radiation from theradiation source.

The mask defines an illumination area of an image to be projected ontothe workpiece using a pattern of the reticle and radiation from theradiation source. The mask includes a plurality of elements configuredto define the illumination area, wherein at least one of the pluralityof elements is positioned above the reticle along a z-axis of thelithographic system, and at least one other of the plurality of elementsis positioned below the reticle along the z-axis of the lithographicsystem.

According to yet another exemplary embodiment of the invention, a methodof operating a lithographic system is provided. The method includes thesteps of: (a) supporting a workpiece using a support structure of thelithographic system; (b) projecting an image on the workpiece usingradiation from a radiation source of the lithographic system; (c)positioning a reticle between the radiation source and the workpiece;(d) positioning a mask adjacent the reticle, the mask being configuredto block radiation from the radiation source; and (e) removing heat fromat least one of the mask and the reticle with a heat removal apparatusof the mask.

According to yet another exemplary embodiment of the invention, anothermethod of operating a lithographic system is provided. The methodincludes the steps of: (a) supporting a workpiece using a supportstructure of the lithographic system; (b) projecting an image on theworkpiece using radiation from a radiation source of the lithographicsystem; (c) positioning a reticle between the radiation source and theworkpiece; and (d) positioning a mask adjacent the reticle, the maskbeing configured to block radiation from the radiation source, whereinthe mask including a body portion and a radiation absorbing coatingapplied to at least a portion of an external surface of the bodyportion.

According to yet another exemplary embodiment of the invention, anothermethod of operating a lithographic system is provided. The methodincludes the steps of: (a) supporting a workpiece using a supportstructure of the lithographic system; (b) projecting an image on theworkpiece using radiation from a radiation source of the lithographicsystem; (c) positioning a reticle between the radiation source and theworkpiece; and (d) positioning a mask adjacent the reticle, the maskbeing configured to block radiation from the radiation source, the maskdefining an illumination area of the projected image using a pattern ofthe reticle and radiation from the radiation source, the illuminationarea defined by the mask being variable.

According to yet another exemplary embodiment of the invention, anothermethod of operating a lithographic system is provided. The methodincludes the steps of: (a) supporting a workpiece using a supportstructure of the lithographic system; (b) projecting an image on theworkpiece using radiation from a radiation source of the lithographicsystem; (c) positioning a reticle between the radiation source and theworkpiece; and (d) positioning a mask adjacent the reticle, the maskbeing configured to block radiation from the radiation source, the maskdefining an illumination area of the projected image using a pattern ofthe reticle and radiation from the radiation source, the mask includinga plurality of elements configured to define the illumination area,wherein at least one of the plurality of elements is positioned abovethe reticle along a z-axis of the lithographic system, and at least oneother of the plurality of elements is positioned below the reticle alongthe z-axis of the lithographic system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity.

FIG. 1 illustrates a side view of a lithographic system in accordancewith an exemplary embodiment of the invention;

FIG. 2 is a perspective view of a portion of a lithographic system inaccordance with an exemplary embodiment of the invention;

FIG. 3A is a top view of a portion of a lithographic system inaccordance with another exemplary embodiment of the invention;

FIG. 3B is a top view of a portion of a lithographic system inaccordance with yet another exemplary embodiment of the invention;

FIG. 3C is a top view of a portion of a lithographic system inaccordance with yet another exemplary embodiment of the invention;

FIG. 4 is a top view of a portion of a lithographic system in accordancewith yet another exemplary embodiment of the invention;

FIG. 5A is a top view of a portion of a mask of a lithographic system inaccordance with an exemplary embodiment of the invention;

FIG. 5B is a top view of a portion of a mask of a lithographic system inaccordance with another exemplary embodiment of the invention;

FIG. 5C is a top view of a portion of a mask of a lithographic system inaccordance with yet another exemplary embodiment of the invention;

FIG. 5D is a top view of a portion of a mask of a lithographic system inaccordance with yet another exemplary embodiment of the invention;

FIG. 5E is a top view of a portion of a mask of a lithographic system inaccordance with yet another exemplary embodiment of the invention;

FIG. 6A is a side view of a portion of a lithographic system inaccordance with an exemplary embodiment of the invention;

FIG. 6B is a side view of a portion of a lithographic system inaccordance with another exemplary embodiment of the invention; and

FIG. 6C is a side view of a portion of a lithographic system inaccordance with yet another exemplary embodiment of the invention.

DETAILED DESCRIPTION

As provided above, in many lithography applications it is desirable toexpose not only full fields but also partial fields (e.g., for alignmentmarks, or edge exposure protection of the workpiece, etc.). Inaccordance with certain exemplary embodiments of the invention, this maybe accomplished using a reticle masking module. Such a module mayinclude four (4) elements/blades (or some other number ofelements/blades) used to define the illumination area of the mask. Inhigh resolution lithography with a high NA (numerical aperture) lens, areticle masking module may be positioned in the illuminator. In alithography system with lower NA it is possible to place the reticlemasking blades close to (adjacent) the reticle. To prevent stray light(and related deleterious effects), the elements/blades of the mask(and/or a blocking part of the reticle) may absorb part of this lightenergy using a light absorbing coating (e.g., an inorganic black coatingwhich absorbs radiation instead of reflecting it, to avoid stray lightresulting in ghost images and the like), leading to high temperaturesaround the reticle. In such cases, it is desirable to have at least oneof the mask (including the aforementioned elements/blades) and thereticle for cooling using a heat reducing element of the mask. This maybe accomplished, for example, by providing internal forced convectioncooling channels in parts of the mask. By adding additional holes in theblade facing the exposed part of the reticle, the same forced convectionair may be used to cool the reticle.

FIG. 1 illustrates a lithographic system 100 for projecting an imageonto a workpiece 104 using radiation. Lithographic system 100 includes asupport structure 102 (e.g., a wafer table) for supporting the workpiece104 (e.g., a wafer, a panel, a rectangular panel or other workpiece,etc.). Lithographic system 100 also includes a radiation source 118(e.g., a mercury lamp, a laser, etc.) for providing radiation to projectan image on the workpiece 104. As shown in FIG. 1 , the radiation(represented by lines including downward pointed arrow heads) passesthrough other elements of lithographic system 100. More specifically,radiation from radiation source 118 passes through a beam deliverysystem 116 and an illuminator 114, both included in lithographic system100. Beam delivery system 116 steers the radiation from radiation source118 to an entrance of illuminator 114, and generally includes suitabledirecting mirrors. Illuminator 114 provides a conditioned beam ofradiation to a reticle 110 having a desired uniformity and intensitydistribution in its cross-section. Downstream of illuminator 114,lithographic system 100 also includes a projection system 106 forprojecting the radiation prior to receipt by workpiece 104.

Reticle 110 is positioned between radiation source 118 and workpiece104. Reticle 110 is supported by a reticle table 108. A reticle pattern110 is provided on reticle 110 (e.g., see reticle pattern 110 a in FIGS.6A-6C). Lithographic system 100 also includes a mask 112 positionedadjacent reticle 110. Mask 112 is configured to block certain radiationfrom radiation source 118 (while other parts of radiation pass throughmask 112 and continue downstream toward workpiece 104. For example, mask112 may define an illumination area of an image to be projected ontoworkpiece 104 using a pattern of reticle 110 and radiation fromradiation source 118.

In accordance with the invention, there are various differentimplementations of mask 112, and its relationship (e.g., spatialrelationship) with reticle 110. FIG. 1 is intended to broadly representthese different implementations. FIG. 2 , FIGS. 3A-3C, FIG. 4 , FIGS.5A-5E, and FIGS. 6A-6C provide specific examples of a mask; each ofthese examples may be included in the configuration of FIG. 1 . Thus,mask 112 in FIG. 1 is illustrated around reticle 110 (e.g., mask 112 maybe above reticle 110, mask 112 may be below reticle 110, mask 112 may bepartially above and partially below reticle 110, etc.).

For example, in accordance with various exemplary embodiments of theinvention, mask 112 may include a plurality of elements (e.g., blades orother elements) collectively defining an illumination area of an imageto be projected onto the workpiece using a pattern of the reticle andradiation from the radiation source. In a specific example, FIG. 2illustrates a mask 112 a including a plurality of elements 112 a 1, 112a 2, 112 a 3, and 112 a 4. Each of elements 112 a 1, 112 a 2, 112 a 3,and 112 a 4 is independently moveable along at least one of the x-axisand the y-axis of lithographic system 100 using respective drivers 202 a1, 202 a 2, 202 a 3, and 202 a 4. In FIG. 2 , the lithographic system100 also includes controller 200 for controlling each of drivers 202 a1, 202 a 2, 202 a 3, and 202 a 4. Through the movement of elements 112 a1, 112 a 2, 112 a 3, and 112 a 4 (via controller 200, and drivers 202 a1, 202 a 2, 202 a 3, and 202 a 4) a desired illumination area is definedby the elements 112 a 1, 112 a 2, 112 a 3, and 112 a 4. Thus, theillumination area may be adjusted as desired to project an image ontothe workpiece using a pattern of the reticle and radiation from theradiation source.

FIGS. 3A-3C are variations of the embodiment described above withrespect to FIG. 2 . In FIG. 3A, a mask 112 b includes a plurality ofelements 112 b 1, 112 b 2, 112 b 3, and 112 b 4. Each of elements 112 b1, 112 b 2, 112 b 3, and 112 b 4 is independently moveable along atleast one of the x-axis and the y-axis of lithographic system 100 usingrespective drivers 302 a 1, 302 a 2, 302 a 3, and 302 a 4 (andcontroller 300 a for controlling each of drivers 302 a 1, 302 a 2, 302 a3, and 302 a 4). Thus, illumination area 304 a defined by mask 112 b maybe adjusted. In FIG. 3A, each of elements 112 b 1, 112 b 2, 112 b 3, and112 b 4 is positioned above reticle 110 along a z-axis of thelithographic system.

In FIG. 3B, a mask 112 c includes a plurality of elements 112 c 1, 112 c2, 112 c 3, and 112 c 4. Each of elements 112 c 1, 112 c 2, 112 c 3, and112 c 4 is independently moveable along at least one of the x-axis andthe y-axis of lithographic system 100 using respective drivers 302 b 1,302 b 2, 302 b 3, and 302 b 4 (and controller 300 b for controlling eachof drivers 302 b 1, 302 b 2, 302 b 3, and 302 b 4). Thus, illuminationarea 304 b defined by mask 112 c may be adjusted. In FIG. 3B, each ofelements 112 c 1, 112 c 2, 112 c 3, and 112 c 4 is positioned belowreticle 110 along a z-axis of the lithographic system.

In FIG. 3C, a mask 112 d includes a plurality of elements 112 d 1, 112 d2, 112 d 3, and 112 d 4. Each of elements 112 d 1, 112 d 2, 112 d 3, and112 d 4 is independently moveable along at least one of the x-axis andthe y-axis of lithographic system 100 using respective drivers 302 c 1,302 c 2, 302 c 3, and 302 c 4 (and controller 300 c for controlling eachof drivers 302 c 1, 302 c 2, 302 c 3, and 302 c 4). Thus, illuminationarea 304 c defined by mask 112 d may be adjusted. In FIG. 3C, each ofelements 112 d 1 and 112 d 3 are positioned above reticle 110, and eachof elements 112 d 2 and 112 d 4 are positioned below reticle 110, alonga z-axis of the lithographic system. By providing a portion of elements112 d 1, 112 d 2, 112 d 3, and 112 d 4 above reticle 110, and anotherportion of elements 112 d 1, 112 d 2, 112 d 3, and 112 d 4 below reticle110, benefits are provided in that a distance between elements 112 d 1,112 d 2, 112 d 3, and 112 d 4 and the reticle pattern (e.g., see reticlepatterns 110 a in FIGS. 6A-6C) is minimized, thus limiting the size ofthe half shadow. The half shadow is the transition from fullyilluminated to fully blocked radiation. The smaller the half shadow, thesmaller the separation on the reticle between the different illuminationpatterns on the reticle.

FIG. 4 illustrates a mask 112 e in relation to reticle 110. Mask 112 eincludes a plurality of body portions 112 e 1, 112 e 2, and 112 e 3(where the plurality of body portions may be formed from a unitary pieceof material or multiple structures). At each respective body portion,mask 112 e defines a corresponding one of illumination areas 404 a 1,404 a 2, and 404 a 3, each of illumination areas 404 a 1, 404 a 2, and404 a 3 being configured to define an image to be projected onto theworkpiece using a pattern of reticle 110 and radiation from theradiation source. Mask 112 e is moveable within an x-y plane oflithographic system 100 using controller 400 and driver 402, to selectfrom among the plurality of illumination areas 404 a 1, 404 a 2, and 404a 3 for present use.

While not required within the scope of the invention, each of FIGS.3A-3C and FIG. 4 is illustrated including a body portion (e.g., part ofthe mask, which may be termed a “heat removal apparatus”) definingcooling channels that receive a cooling fluid from a fluid source (notshown), and that direct the cooling fluid (e.g., a cooling air, shown as“AF” for air flow) toward the reticle.

Thus, in certain exemplary embodiments of the invention, mask 112includes a “heat removal apparatus”. Such a heat removal apparatus,within the scope of the invention, may be any type of system or elementfor removing heat from at least one of the mask and the reticle.Examples of such a heat removal apparatus include: (a) a body portion ofthe mask defining at least one cooling channel configured to receive acooling fluid from a fluid source, where the cooling fluid (e.g., air,etc.) is directed toward the reticle; (b) a body portion of the maskdefining at least one cooling channel configured to receive a coolingfluid from a fluid source, where the cooling fluid (e.g., air, liquid,etc.) is provides cooling of the mask; (c) a heat sink coupled (e.g.,via a conductive braid) to a body portion of the mask; and (d) a pipecoupled to a body portion of the mask, the pipe configured to direct acooling fluid towards the reticle. Of course, other heat removalapparatuses are contemplated within the scope of the invention.

FIG. 5A is a top view of an element 112′a (e.g., a blade) of a mask—suchas any of masks 112 a, 112 b, 112 c, 112 d, and 112 e shown in FIGS. 2,3A-3C, and 4 . Element 112′a includes a body portion 500 a defining aplurality of cooling channels 502 a configured to receive a coolingfluid from a fluid source (where the fluid enters via “inlet” from thefluid source, not shown), where the cooling fluid (e.g., air, or anothercooling gas) exits body portion 500 a via outlets 502 a 1 and isdirected toward the reticle (such as shown with arrows “AF”, also inFIGS. 2, 3A-3C, and 4 ).

FIG. 5B is a top view of an element 112′b (e.g., a blade) of a mask—suchas any of masks 112 a, 112 b, 112 c, 112 d, and 112 e shown in FIGS. 2,3A-3C, and 4 . Element 112′b includes a body portion 500 b defining aplurality of cooling channels 502 b configured to receive a coolingfluid from a fluid source (where the fluid enters via “inlet” from thefluid source, not shown), where the cooling fluid (e.g., air, or anothercooling gas) exits body portion 500 b via outlets 502 b 1 and isdirected toward the reticle (such as shown with arrows “AF”, also inFIGS. 2, 3A-3C, and 4 ). FIG. 5B differs from FIG. 5A in that thecooling channels 502 b are distributed through a more significant partof body portion 500 b prior to reaching outlets 502 b 1. That is, inFIG. 5B, an intentional cooling function is provided to this part ofbody portion 500 b prior to the cooling fluid exiting body portion 500 bvia outlets 502 b 1.

FIG. 5C is a top view of an element 112′c (e.g., a blade) of a mask—suchas any of masks 112 a, 112 b, 112 c, 112 d, and 112 e shown in FIGS. 2,3A-3C, and 4 . Element 112′c includes a body portion 500 c defining aplurality of cooling channels 502 c configured to receive a coolingfluid from a fluid source (where the fluid enters via “inlet” from thefluid source, not shown), where the cooling fluid (e.g., air, or anothercooling gas) exits body portion 500 c via outlets 502 c 1 and isdirected toward the reticle (such as shown with arrows “AF”, also inFIGS. 2, 3A-3C, and 4 ). Like FIG. 5B, in FIG. 5C the cooling channels502 c are distributed through a more significant part of body portion500 c prior to reaching outlets 502 c 1 to provide the cooling functionto this part of body portion 500 c. Further, in FIG. 5C, coolingchannels 502 c includes a return channel for directing cooling fluidback to the fluid source via “return” (the fluid source is not shown forsimplicity).

FIG. 5D is a top view of an element 112′d (e.g., a blade) of a mask—suchas any of masks 112 a, 112 b, 112 c, 112 d, and 112 e shown in FIGS. 2,3A-3C, and 4 . Element 112′d includes a body portion 500 d defining aplurality of cooling channels 502 d configured to receive a coolingfluid from a fluid source (where the fluid enters via “inlet” from thefluid source, not shown), where cooling fluid (e.g., air, liquid, oranother cooling fluid) is distributed through a more significant part ofbody portion 500 d prior to returning to the fluid source via one ormore return channels for directing the cooling fluid back to the fluidsource via “return” (the fluid source is not shown for simplicity).

FIG. 5E is a top view of an element 112′e (e.g., a blade) of a mask—suchas any of masks 112 a, 112 b, 112 c, 112 d, and 112 e shown in FIGS. 2,3A-3C, and 4 . Element 112′e includes a body portion 500 e, and aseparate heat sink 504 coupled to body portion 500 e of the mask. In theexample shown in FIG. 5E, heat sink 504 is coupled to the body portion500 e via conductive braid 506. Heat sink may include active cooling(e.g., air cooling, etc.) and/or may include static cooling elementssuch as cooling fins or the like.

In another example a heat removal apparatus may include a pipe (or othercooling fluid carrying structure) coupled to a body portion of a mask,where the pipe is configured to direct a cooling fluid towards thereticle.

FIGS. 6A-6C are side view block diagram illustrations showing examplesof cooling fluid being directed towards a reticle, where suchillustrations may be applicable to any embodiment of the inventiondirecting such cooling fluid towards a reticle (e.g., FIG. 2 , FIGS.3A-3C, FIG. 4 , FIGS. 5A-5C, among others). In FIG. 6A, radiation(“RADIATION”) is provided from above (e.g., from radiation source 118shown in FIG. 1 ). Element 112′ of a mask (e.g., a blade) includescooling channel 502′, through which a cooling fluid “AF” travels and isdirected toward reticle 110 (including reticle pattern 110 a) via outlet502″.

FIG. 6B is similar to FIG. 6A (with like reference numbers) except thata radiation absorbing coating 600 (e.g., an inorganic black coating) hasbeen applied to at least a portion of an external surface of the bodyportion of element 112′a. This coating absorbs some of the radiation(“RADIATION”) coming from radiation source 118 (e.g., see FIG. 1 ),undesirably resulting in heating at or around reticle 110 (includingreticle pattern 110 a). The cooling fluid “AF” travelling in coolingchannel 502′a (and exiting outlet 502″a) provides a cooling function toat least partially address this heating.

FIG. 6C illustrates an element 112′ (as in FIG. 6A), but in FIG. 6C pipe602 (defining path 602′ for cooling fluid) is coupled (either directlyor indirectly) to element 112′. Cooling fluid “AF” travels in path 602′,and exits element 112′ at outlet 602″, being directed at reticle 110(including reticle pattern 110 a).

In accordance with various exemplary embodiments of the invention, amask of a lithographic system is positioned adjacent the reticle. Withrespect to the z-axis of the lithographic system, the term “adjacent” isintended to mean at least one of: (a) the mask being within 100 mm ofthe reticle along the z-axis; (b) the mask being within 50 mm of thereticle along the z-axis; (c) the mask being within 30 mm of the reticlealong the z-axis; and (d) the mask being within 10 mm of the reticlealong the z-axis.

Although the invention has been described and illustrated with respectto the exemplary embodiments thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, without partingfrom the spirit and scope of the present invention. Rather, variousmodifications may be made in the details within the scope and range ofequivalents of the claims and without departing from the invention.

What is claimed:
 1. A method of operating a lithographic system, themethod comprising the steps of: (a) supporting a workpiece using asupport structure of the lithographic system; (b) projecting an image onthe workpiece using radiation from a radiation source of thelithographic system; (c) positioning a reticle between the radiationsource and the workpiece; and (d) positioning a mask adjacent thereticle, the mask being configured to block radiation from the radiationsource, wherein the mask including a body portion and a radiationabsorbing coating applied to at least a portion of an external surfaceof the body portion.
 2. The method of claim 1 wherein step (d) includespositioning the mask within 100 mm of the reticle along a z-axis of thelithographic system.
 3. A method of operating a lithographic system, themethod comprising the steps of: (a) supporting a workpiece using asupport structure of the lithographic system; (b) projecting an image onthe workpiece using radiation from a radiation source of thelithographic system; (c) positioning a reticle between the radiationsource and the workpiece; and (d) positioning a mask adjacent thereticle, the mask being configured to block radiation from the radiationsource, the mask defining an illumination area of the projected imageusing a pattern of the reticle and radiation from the radiation source,the illumination area defined by the mask being variable.
 4. The methodof claim 3 wherein the mask includes a plurality of elements configuredto define the illumination area, at least one of the plurality ofelements being moveable with respect to others of the plurality ofelements such that the illumination area is variable.
 5. A method ofoperating a lithographic system, the method comprising the steps of: (a)supporting a workpiece using a support structure of the lithographicsystem; (b) projecting an image on the workpiece using radiation from aradiation source of the lithographic system; (c) positioning a reticlebetween the radiation source and the workpiece; and (d) positioning amask adjacent the reticle, the mask being configured to block radiationfrom the radiation source, the mask defining an illumination area of theprojected image using a pattern of the reticle and radiation from theradiation source, the mask including a plurality of elements configuredto define the illumination area, wherein at least one of the pluralityof elements is positioned above the reticle along a z-axis of thelithographic system, and at least one other of the plurality of elementsis positioned below the reticle along the z-axis of the lithographicsystem.
 6. The method of claim 5 wherein (i) the plurality of elementspositioned above the reticle along the z-axis includes a pair ofelements configured to move with respect to one another along an x-axisof the lithographic system and (ii) the plurality of elements positionedbelow the reticle along the z-axis includes a pair of elementsconfigured to move with respect to one another along a y-axis of thelithographic system.